Congestion is a networking term that refers to a situation where too much network traffic is clogging network pathways. Common causes of congestion may include too many users being active on a single network segment or collision domain, high demand from bandwidth-intensive networked applications, a rapidly growing number of users accessing the Internet, the increased power of personal computers (PCs) and servers, etc.
One common indicator of network congestion is increased network delay. All networks have a limited data-carrying capacity. When the load is light, the average time from when a host submits a packet for transmission until it is actually sent on the network is relatively short. When many users are vying for connections and communicating, the average delay increases. This delay has the effect of making the network appear “slower,” because it takes longer to send the same amount of data under congested conditions than it does when the load is light. In extreme circumstances, an application can fail completely under a heavy network load. Sessions may timeout and disconnect, and applications or operating systems may actually crash, requiring a system restart.